Introduction

Low-temperature nitriding of austenitic stainless steels allows for the formation of a supersaturated solid solution of nitrogen in the austenite lattice (expanded austenite or S-phase), while inhibiting the precipitation of Cr nitrides. The corrosion behavior of the nitrided layers depends on their microstructure and phase composition, as well as on the environment characteristics. The testing conditions can also play a role, as observed when the repassivation characteristics are assessed. The aim of the present study is to evaluate the corrosion behavior of low-temperature nitrided AISI 316L austenitic stainless steel using different electrochemical techniques and, in particular, to assess the repassivation capability in NaCl solution.

Methods

AISI 316L samples were glow-discharge-nitrided at 380 °C, under 130 Pa, for 5 h. Microstructure, phase composition, and surface microhardness were assessed. Corrosion behavior was evaluated in 5 wt.% NaCl aerated solution using different electrochemical techniques (electrochemical impedance spectroscopy (EIS), cyclic potentodynamic, and galvanostatic techniques).

Results

The hardened nitrided layers mainly consisted of expanded austenite. EIS analysis showed that nitrided samples had higher impedance values than the untreated steel. The cyclic potentiodynamic test results were affected by testing conditions. Corrosion potential and pitting potential values of the nitrided samples were higher than those of the untreated ones, but the nitrided samples were not capable of repassivating. On the contrary, when the galvanostatic technique was employed, the potential value, below which localized corrosion phenomena did not occur, was usually higher than the corrosion potential of the untreated alloy, suggesting that repassivation could occur.

Conclusions

The experimental results suggested that the repassivation capability of nitrided AISI 316L austenitic stainless steel was particularly sensitive to the extent of damage. When minor damage occurred, from, for example, using the galvanostatic technique, high corrosion resistance was maintained. However, fairly significant corrosion damage, such as that occurring in cyclic potentiodynamic tests, hindered repassivation.

Flash-Plasma Electrolytic Oxidation (Flash-PEO) is short anodizing surface treatment that has demonstrated outstanding corrosion resistance associated with self-healing mechanisms. However, similarly to conventional PEO, there is a limitation regarding the incorporation of certain species in the composition of the PEO coating. In that direction, precursor-driven functionalization is a novel approach that can be used in place of the classical one, where the final composition only depends on the electrolyte and the metal.

In this work, a commercial permanganate–fluorozirconate conversion coating (ZrCC) has been used as a precursor prior to a silicate–fluoride (SiF) Flash-PEO treatment. Coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), or X-ray photoelectron spectroscopy (XPS). The corrosion performance was evaluated by open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) after immersion in 0.5 wt. % NaCl. Results have revealed an improvement in the corrosion resistance up to 72h due to Zr and Mn incorporation as well as changes in the porosity and compactness of the Flash-PEO layer.

In summary, the use of precursors such as ZrCC (source of Zr and Mn cations) has been confirmed as an efficient strategy to vary the chemical composition of Flash-PEO coatings, improving their corrosion resistance.

In view of sustainable-by-design issues, there is an urgent need to replace harmful coating ingredients with more ecological, non-toxic alternatives derived from bio-based resources. In particular, fluorine derivatives such as polytetrafluoroethylene (PTFE) are frequently applied in coatings because of their versatile role in rendering hydrophobicity and lubrication. In this research, a screening study is presented on the performance of alternative biowaxes derived from different natural sources, when used in protective coating applications. Micronized powders from carnauba wax, rapeseed wax, rice bran wax, palm oil wax, or sunflower wax are added into epoxy clear-coat formulations. When dispersed into a bio-based epoxy from epoxidized flaxseed oil and a proprietary acid hardener, the thermal curing process significantly affects the efficiency of the biowax additives. In concentration ranges of 1 to 10 wt. %, it was observed that the biowaxes consequently present higher hardness and hydrophobicity as coatings as compared to the PTFE additives, while similar abrasive resistance and scratch resistance could be obtained. Moreover, the proprietary mixture ratios of biowax to PTFE powders provide synergistic effects. The granulometry of the biowax powders is a crucial parameter as smaller micrometer grain sizes improve dispersibility in the coating. The mechanistic effects of micronized biowax powder in the epoxy coating are further evaluated through spectroscopic analysis, indicating their interference with the curing process of the epoxy coating.

Coating technology involves the application of a thin layer of material onto a substrate to enhance its surface properties, including protection, functionality, and aesthetics. Coatings can be made from various materials such as polymers, pigments, additives, and solvents, depending on the intended application. These coating layers serve multiple purposes, such as providing corrosion resistance, improving wear durability, reducing friction, or offering thermal and electrical insulation. The development of sustainable coating technologies is essential to addressing environmental, economic, and social challenges associated with conventional coatings. Traditional coatings often rely on petroleum-based resources and volatile organic compounds (VOCs), contributing to greenhouse gas emissions, air pollution, and health hazards. As global industries strive to reduce their environmental carbon footprint, the demand for eco-friendly coating alternatives has grown significantly.

Therefore, a biochar-based sustainable coating has been developed to achieve a sustainable alternative for conventional coatings. Biochar from different sources of biomasses were prepared by pyrolysis at varying conditions and characterized by FTIR, FESEM, BET, XRD, etc. Derived biochar offers unique properties such as high thermal stability and chemical inertness, making it an effective component for corrosion protection. When this biochar is incorporated into coating formulations, it forms a barrier that inhibits the diffusion of corrosive agents like water, oxygen, and chlorides to metal surfaces. Additionally, the carbon-rich structure of biochar enhances the durability of coatings and provides cathodic protection, reducing metal oxidation rates. These coatings have potential applications in industries such as the infrastructure, marine, and automotive sectors, where corrosion resistance is critical. Beyond these benefits, biochar-based coatings promote environmental sustainability by utilizing renewable biomass resources and reducing reliance on petroleum-based materials. However, further research is needed to optimize coating techniques and evaluate the long-term stability and environmental impacts of biochar-coated products.

UV curing technology is widely used in the furniture, plastic and printing industries. An interesting application of this technique may also be in the future protection of cultural heritage, with a specific focus on metal artifacts. The growing interest in this curing technique is due to its numerous advantages, including low energy consumption, almost zero volatile organic compounds (VOCs) and fast production speed. The use of UV-cured coatings on metal substrates is still very limited, despite many advances made in recent years. The main problems are a lack of adhesion to the substrate or limited corrosion resistance.

The essence of this research is to develop a new method for obtaining and determining the properties of biobased, (meth)acrylated, acidic adhesion promoters. Based on the results of the conducted studies, the conditions for the synthesis process were selected, raw materials were selected for obtaining new biobased adhesion promoters and their properties were tested. The assumed structure of the obtained compounds was confirmed and their basic properties were determined. The use of raw materials from renewable sources to obtain new adhesion promoters was also justified due to issues of environmental protection and sustainable development. Traditional commercial adhesion promoters were also selected for comparative studies.

Acknowledgments

This research was carried out under the project BiBACoM 01/36/CORNET/BIBACOM “Bio-Based UV-Curable Anti-Corrosion Coatings for Metal Substrates” funded by the National Centre for Research and Development (NCBR).

Mango (Manguifera indica var. Azúcar) is known for its distinctive aroma and flavor that contrast with a short shelf life due to the fruit being highly perishable; thus, it is necessary to find mechanisms that help us extend its shelf life. Currently, the use of biopolymers obtained from plant sources as biodegradable, renewable, and low-cost materials for food packaging, combined with the use of essential oils obtained from plant matrices, is capable of improving mangoes' antioxidant, antimicrobial, and barrier properties. We evaluated the effect of the application of a composite edible coating from cassava–Arabic gum incorporated with oregano essential oil for the preservation of fresh-cut mango. A composite edible coating was prepared with different concentrations of cassava hydrocolloids (4, 6, and 8% w), Arabic gum (1%), and oregano essential oil (0.25 and 0.5% v/v). The physical properties of the coating solution were analyzed (color, rheology, and microstructure). Then, the composite edible coating was applied by dipping fresh-cut slices of mango into it, and these were stored for 30 days. The water loss, pH, titratable acidity, total solids, and color were evaluated. The experimental data were adjusted to a zero-order kinetic model. The composite edible coating solution presented non-Newtonian shear thinning behavior described by the Carreau–Yasuda model. Coated mango pieces with the highest addition of essential oil demonstrated a decrease of up to 10% in water loss rate and improved preservation of total solids and acidity, leading to a lower difference in color (ΔE) compared to the uncoated sample for up to 30 days. The results suggest that the application of this coating can extend the shelf life of this minimally processed product.

The issue of fire protection for buildings is prevalent primarily in public buildings. The building products used must be flame-resistant or non-combustible, depending on their place of use.

The topic of this presentation concerns innovative coatings for the fire protection of structural elements used in modern modular construction in order to increase their fire safety.

The developed products for painting modular building elements allow for the passive fire protection of structural elements thanks to their ability to delay the ignition of materials covered with them by reducing the spread of flames.

One of the directions we have taken in obtaining fire-retardant paint products was to replace toxic halogen systems with systems based on phosphorus compounds, which allow for their safe use in public buildings.

The focus of this study was on transparent products with short curing times. Both 1K and 2K water-borne and solvent-borne products were selected for testing.

A 2K PUR varnish based on a modified acrylic resin, a 2K epoxy varnish based on a modified epoxy resin, and a water-based varnish based on an acrylic dispersion resin were developed. A 20% addition of active flame-retardant fillers (polyphosphate and polyols derivatives) was introduced to each product.

The obtained varnishes exhibited excellent resistance to open flame exposure. The tests were conducted using a test stand to examine the ignitability of products under the influence of a small flame, in accordance with EN ISO 11925-2:2020.

In conclusion, during the research process, transparent flame-retardant varnishes for wooden substrates, both water-borne and solvent-based, were successfully developed. Careful selection of active fillers as retardants allowed the creation of user-friendly, easy-to-apply, and environmentally friendly products with high fire resistance.

This work was financially supported by the Łukasiewicz Research Network Centre (Poland), Grant number: 1/Ł-IMPiB/CŁ/2021

Muralism is becoming increasingly significant in the field of urban art and a symbol of a city’s identity. The works are endangered by diverse factors including vandalism and meteorological agents, among others. Consequently, the necessity to find methods to lessen degradation such as fading or cracking emerges.

This study evaluated the physical, chemical and mineralogical changes in two acrylic fluorescent and four alkyd paints applied to concrete samples under different conditions: samples with a pre-coating and/or colour protectors (varnishes manufactured by Proa or Ega and commonly used to protect murals). Thus, six conditions (paint-only, paint with Proa, paint with Ega, paint with pre-coating, paint with pre-coating and Proa, and paint with pre-coating and Ega) were assessed. In addition, paints, concrete, and protective products were mineralogically and chemically characterized by X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. A total of 36 samples were exposed to the QUV accelerated weathering test for 1512h, and throughout the test, colour monitoring was carried out. After the exposure period, a multi-analytical evaluation based on stereomicroscopy, contact angle measurement, peeling tests, XRD, FTIR and scanning electron microscopy coupled with energy-dispersive spectroscopy was conducted.

The findings suggested that the orange alkyd and fluorescent (orange and green) paints experienced the most noticeable colour changes while the green alkyd paints were the most resistant. Unexpectedly, the colour differences at the end of the test were not slowed down by the fixing primer. Using a colour protector might help preserve murals. Even though both protectors studied altered the original colour, Proa was the most effective in terms of colour reduction, but it caused more intense craquelure and the existence of tiny whitish Ti-enriched deposits.

Multifunctional coatings for the protection and conservation of built cultural heritage are extremely useful for addressing the several and different degradation mechanisms that develop and threaten natural stones, which are exposed to environmental conditions. This study presents the development of a nanocomposite coating, consisting of zinc oxide (ZnO) nanoparticles and a polysiloxane binder, designed to protect limestone heritage by integrating three key properties: extreme water resistance, self-cleaning, and antimicrobial action. According to images obtained by Optical Profilometry, nanoparticles play a crucial role in forming a hierarchical, lotus-inspired structure and increasing surface roughness that imparts enhanced water-repellent properties. Since water is a primary factor in the deterioration of natural limestone, achieving effective water resistance is essential for its preservation. Notably, the wetting properties of the polysiloxane–ZnO composite are comparable with the wettabilities of other composite superhydrophobic coatings, consisting of polysiloxanes and silicon oxide (SiO₂) nanoparticles, which were developed in the past. The polysiloxane selected herein serves two purposes simultaneously: first, it acts as a binder for the nanoparticles, and second, it contributes to the consolidation of the stone. ZnO was selected, instead of other nanoparticles (e.g. SiO₂), because it has photocatalytic and antibacterial properties. The self-cleaning scenario is demonstrated with experiments, which were conducted using methylene blue as a model contaminant. Moreover, it is shown that the suggested coating hinders the incubation of E. coli and S. aureus. Extensive experiments confirm that the designed coating exhibits excellent mechanical, chemical, and thermal stability.

Fibrous plaster is a historic material of great prevalence within theaters and auditoriums within the UK, but until recently it has been almost completely unresearched. With the partial collapse of the Apollo Theatre ceiling in 2013, there is growing interest in the safe conservation of fibrous plaster. This study investigates the architectural paint coatings originally applied to fibrous plaster sampled from five London theatres and auditoriums built between 1856 and 1919.

A rigorous analysis of the individual paint layers was conducted using carefully prepared polished cross-sections. The finishes applied were identified using state-of-the-art characterisation techniques, including digital microscopy, SEM imaging, SEM-EDX mapping, Raman spectroscopy, Fourier transform infrared spectroscopy, and water solubility testing. The investigations demonstrated that for 20th-century theatres, lead white oil paint has been shown to constitute their early finish history, whereas venues built before the turn of the century were originally decorated with other materials, including distemper, gold size, and gilding.

This is the first systematic research on architectural finishes originally used on fibrous plaster. The results provide important physical and chemical information relating to the coatings used, informing on the most appropriate conservation approaches. It provides a foundation upon which further investigation into this under-researched material can be based.